It's a trick question. Both sentences are correct. The use to the serial comma is a grammar suggestion not a rule. Mostly it depends on the type of writing in question. There are even differences in it's usage between the various English dialects.

In the example you give you are correct, HOWEVER, if the items are equal in nature and do not denote numbers you are not required to separate the last listed item before the "and". The trick is to be consistent so that your reader knows that you are using the comma to replace the linking word.

In the example you give you are correct, HOWEVER, if the items are equal in nature and do not denote numbers you are not required to separate the last listed item before the "and". The trick is to be consistent so that your reader knows
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In the example you give you are correct, HOWEVER, if the items are equal in nature and do not denote numbers you are not required to separate the last listed item before the "and". The trick is to be consistent so that your reader knows that you are using the comma to replace the linking word.

It's a trick question. Both sentences are correct. The use to the serial comma is a grammar suggestion not a rule. Mostly it depends on the type of writing in question. There are even differences in it's usage between the various English dialects.